Heretofore, power divider-combiner circuits of this type have often been adopted in high-frequency power amplifiers or mixer circuits requiring division and combination of power.
For example, Japanese Unexamined Patent Application Publication No. 11-127004 discloses a compact high-frequency circuit having a superior amplitude balance. However, this high-frequency circuit is not preferable because a reduction in occupied area is required for downsizing.
The high-frequency circuit disclosed in the publication is shown in, for example, FIG. 1. One end of a power divider-combiner 21 shown in FIG. 1 is connected to an I/O port P1, and the other end of the power divider-combiner 21 is connected to I/O ports P2 and P3 via transmission lines 22 and 23, respectively.
Each of the three I/O ports P1 to P3 has an I/O impedance of 50 Ω, and each of the transmission lines 22 and 23 has a characteristic impedance of 50 Ω. The line length δ of the transmission line 22 differs from the line length (δ+θ) of the transmission line 23 by an amount θ and the difference θ in line length corresponds to a difference in electrical length. In a drawing shown in the publication, a resistor 24 is connected in series to the transmission line 22, as in FIG. 1. As also shown in the drawing (e.g., see α of FIG. 1) and described in the publication, the power divider-combiner 21 generates a phase difference of α (in degrees) between its two outputs.
In this structure, a signal input through the I/O port P1 is divided into two signal components (one having a phase equal to 0 and the other having a phase equal to −α) by the power divider-combiner 21 and the output is halved. One of the signal components (the one having the phase equal to 0), having the halved output, is supplied to the I/O port P2 through the transmission line 22. The other of the signal components (the one having the phase equal to −α) is supplied to the I/O port P3 through the transmission line 23. The transmission line 22 differs from the transmission line 23 in the line length by the amount θ. Accordingly, the phase of the signals through the transmission line 22 is shifted from that of the signals through the transmission line 23 by an amount corresponding to the difference θ in electrical length while the signals of the same size are supplied to the I/O ports P2 and P3. For example, if “θ” is equal to zero, the phase difference becomes zero. If “θ” is equal to ¼ of a wavelength λ of the signals, the phase difference becomes 90°. If “θ” is equal to ½ of the wavelength λ of the signals, the phase difference becomes 180°.
In contrast, the signals input through the I/O ports P2 and P3 are supplied to the power divider-combiner 21 through the transmission lines 22 and 23 and are combined with each other by the power divider-combiner 21, and the combined signal is output through the I/O port P1.
Although the power divider-combiner 21 of a Wilkinson type is ordinarily used, the power divider-combiner 21 of a branch-line type or of a rat-race type may be used depending on the application.
The resistor 24 provided in FIG. 1 compensates for the difference in the resistances of the transmission lines in the division to eliminate differences in transmission loss and in amplitude. As a result, the circuit having a superior balance is realized.
The power divider-combiner circuit having the above structure occupies a larger area in the amplifier and, therefore, is inevitably expensive, regardless of the Wilkinson circuit, the branch-line circuit, or the rat-race circuit. This is because, for example, even the Wilkinson circuit having the smallest occupied area has transmission lines having an electrical length that is at least “half” of the wavelength λ of the signals. Furthermore, since the resistor and the transmission lines for adjusting the differences in amplitude and phase are provided, the circuit inevitably has a larger size.
In order to resolve the above problems, an object of the present invention is to provide a power divider-combiner circuit which has a simple structure in order to reduce in size and which is capable of realizing a reduction in cost.